Deoxidizer solutions are used to treat the surfaces of various metals and metal alloys by deoxidizing, desmutting and/or etching the surface of the treated metal or metal alloy. Deoxidizer solutions are particularly useful for treating metals and metal alloys prior to anodizing, conversion coating, bonding and welding. For example, aluminum and aluminum alloys are commonly treated with a deoxidizer solution prior to anodizing to lower the surface resistance of the material.
Deoxidizer solutions typically include strong acids that are optionally fortified with various beneficial metal ions. For example, prior to anodizing, an aluminum substrate is commonly treated with a deoxidizer solution that includes a strong nitric acid solution fortified with iron ions. A commercially available example of such a deoxidizer solution for treating aluminum substrates is prepared by blending water and 42° Baume nitric acid with a quantity of TURCO® ALDOX V solution, which is available from Henkel Surface Technologies of Madison Heights, Mich. The TURCO® ALDOX V solution introduces iron ions to the deoxidizer solution.
After repeated use, a deoxidizer solution may become contaminated with undesirable metal ions that may diminish the treatment effect of the deoxidizer solution. For example, the water, nitric acid and TURCO® ALDOX V solution mixture discussed above may become contaminated with copper ions after being repeatedly used to treat aluminum alloys. Copper ion concentrations in excess of about 200-300 parts per million, certainly concentrations in excess of 600 parts per million, substantially inhibit the treatment effect of such deoxidizer solutions. Therefore, once a threshold contamination level has been reached, the contaminated deoxidizer solution must be discarded and a fresh deoxidizer solution must be prepared, thereby presenting the user with hazardous waste disposal costs in addition to the cost associated with preparing fresh deoxidizer solution.
Accordingly, those skilled in the art continue to look for techniques for selectively removing certain undesirable ions, such as copper ions, from acidic solutions.